1. Technical Field of the Invention
The present invention relates to an image reader for reading an image drawn on a document, and more particularly, to an image reader which can effect reading operations in both of a flat bed reading mode and a sheet through reading mode and read a document at high speed.
2. Description of the Related Art
In the field of an image reader used in a scanner, a facsimile, or the like, an image reader which can read a document in both a flat bed mode and a sheet through mode has conventionally been known (see, e.g., below mentioned Japanese Patent Documents 1 through 3). Here, the flat bed mode is a mode in which a lower surface of a document is scanned by a moving image sensor from below a platen plate to optically read an image on the document while a surface of the document to be read is placed and oriented downward on the platen plate provided on top of a document table. Further, the sheet through mode is a mode in which a document moving mechanism causes a document to move through a transport path and reads an image on the document by means of the image sensor while the document is moving.
FIG. 9 is a cross-sectional view of the principal feature of the conventional document reader (see Patent Document 1).
In FIG. 9, the conventional image reader is provided with a platen glass 101 placed on top of a document table 100. An image sensor 102 having a charge-coupled element (CCD) is provided in the document table 100 so as to be movable in parallel with the platen glass 101.
A document table cover 103 is pivotally supported at one end of the document table 100 (hereinafter, a side of the document table 100 pivotally supporting the document table cover 103 is called a “rear side,” and the opposite side of the document table 100 is called a “front side”). A base end section of the document table cover 103 incorporates an automatic paper feeder 104. A hopper unit 105 to be used for loading documents to be fed is disposed at an upper front portion of the automatic paper feeder 104. Moreover, a recovery tray 106 is provided below the hopper unit 105. Provided in the automatic paper feeder 104 is a C-shaped transport guide 107 which extends from the hopper unit 105 to the recovery tray 106.
A paper feed roller 108 for feeding the document placed on the hopper unit 105 to the transport guide 107 is provided in an upper section of the entrance of the transport guide 107 (i.e., a portion of the transport guide 107 opened for the hopper unit 105). Further, a separation roller 109 and a retard roller 110 are provided so as to vertically, closely oppose each other at a position downstream of the transport guide 107 and adjacent to the paper feed roller 108. A plurality of transport rollers 111 to be used for transporting the document are provided along the transport guide 107.
When an image is read in a flat bed mode, the image sensor 102 reads an image on the document that is situated on the platen glass 101 so as to face downward, while moving below the platen glass 101 by means of a sensor drive mechanism (not shown).
When an image is read in the sheet through mode, the document is fed along the transport guide 107 while the image sensor 102 is situated stationary at the rear end section of the document table 100. A track of the document within the transport guide 107 passes through a focal point of the stationary image sensor 102 (hereinafter called a “scan point”). Therefore, when the document passes through the scan point, the image on a lower surface of the document is read by the image sensor 102. The document that has finished undergoing image reading operation is output to the recovery tray 106.
As mentioned above, reading of an image of a document is implemented in the flat bed mode and the sheet through mode by means of a single image sensor 102.
[Patent Document 1] JP-A-2000-159393
[Patent Document 2] JP-A-2000-307821
[Patent Document 3] JP-A-11-32163
However, the conventional image reader reads only one side of the document when an image on the document is read in the sheet through mode. Therefore, when images drawn on both sides of the document are read, an image on one side of the document is read first. Then, an image on the other side of the document is to be read by turning the document inside out. Therefore, reading of the document involves consumption of time.
Depending on the particular document, the document may have a large thickness and high flexural rigidity, like a piece of cardboard. When an attempt is made to read such a document, the document may be caught by the inside of the transport guide 107, to thereby cause a paper jam, while passing through the transport guide 107 bent like a letter C.